1. Field of the Invention
The present invention relates generally to high molecular weight drag reducers for use in crude oils. In another aspect, the present invention relates to high molecular weight drag reducing polymers for use in crude oils having an asphaltene content of at least about 3 weight percent and an API gravity of less than about 26°.
2. Description of the Prior Art
When fluids are transported by a pipeline, there is typically a drop in fluid pressure due to friction between the wall of the pipeline and the fluid. Due to this pressure drop, for a given pipeline, fluid must be transported with sufficient pressure to achieve the desired throughput. When higher flow rates are desired through the pipeline, more pressure must be applied due to the fact that, as flow rates are increased, the difference in pressure caused by the pressure drop also increases. However, design limitations on pipelines limit the amount of pressure that can be employed. The problems associated with pressure drop are most acute when fluids are transported over long distances. Such pressure drops can result in inefficiencies that increase equipment and operation costs.
To alleviate the problems associated with pressure drop, many in the industry utilize drag reducing additives in the flowing fluid. When the flow of fluid in a pipeline is turbulent, high molecular weight polymeric drag reducers can be employed to enhance the flow. A drag reducer is a composition capable of substantially reducing friction loss associated with the turbulent flow of a fluid through a pipeline. The role of these additives is to suppress the growth of turbulent eddies, which results in higher flow rate at a constant pumping pressure. Ultra-high molecular weight polymers are known to function well as drag reducers, particularly in hydrocarbon liquids. In general, drag reduction depends in part upon the molecular weight of the polymer additive and its ability to dissolve in the hydrocarbon under turbulent flow. Effective drag reducing polymers typically have molecular weights in excess of five million.
Conventional polymeric drag reducers, however, typically do not perform well in crude oils having a low API gravity and/or a high asphaltene content. Accordingly, there is a need for improved drag reducing agents capable of reducing the pressure drop associated with the turbulent flow of low API gravity and/or high-asphaltene crude oils through pipelines.